The present invention relates to a measuring apparatus provided with a stylus or a probe. The invention more particularly concerns an apparatus including a sliding carriage and a stylus carrier, secured to the carriage and on which the stylus is mounted. In the apparatus according to the invention, the stylus carrier includes a metal bar of a polygonal cross section with at least two plane faces, and a support which is secured to one of the ends of the bar and on which the stylus is secured, the other end of the bar being mounted on the carriage.
An apparatus of this type is disclosed in U.S. Pat No. 5,072,522. This apparatus includes a base and a column secured to the base. A carriage is mounted so as to slide on the column and it is connected to a counterbalance weight, so that it remains in any position between the two ends of the column. A stylus is mounted on a stylus carrier, which is itself secured to the carriage. U.S. Pat. No. 5,072,522 neither describes nor shows the means for securing the stylus carrier onto the carriage.
UK Patent No. 2 039 673 discloses an entirely comparable apparatus. In this case, the stylus carrier is secured to the carriage by a U-shaped part and a knurled screw screwed into the carriage. Such a solution certainly allows the stylus carrier to be rigidly connected onto its support. However, the replacement of the stylus carrier poses a problem, since the position of the stylus carrier set in place cannot be guaranteed. It is thus necessary to begin by orienting the stylus carrier approximately, then re-calibrating the apparatus before being able to effect a new measurement. Moreover, the tightening torque may vary considerably from one person to another, so that the rigidity of the assembly can be problematic. Such a solution is not sufficient if one wishes to be able to effect successive measurements with several stylus carriers, without having to effect long adjustments.
The main object of the present invention is to allow a stylus carrier to be quickly and precisely set in place on such an apparatus.
This object is achieved as a result of the fact that the carriage of the device according to the invention is provided with a slide, having a cross section into which the cross section of the bar fits, which includes a first end in which the bar is engaged provided with two supports arranged longitudinally on one of the sides of the slide, one at each of its ends, and intended to be in contact with one of the faces of the bar. A locking member formed of a lock cooperates with the other face. A spring generates a blocking force which applies the lock against the bar, the force being oriented along an axis passing between the two supports. Advantageously, the bar is of rectangular cross section the sides of which have a ratio between 1/3 and 1/5.
In a particularly simple and efficient embodiment, the lock is formed of a cylindrical rod provided with a flat side parallel to the axis of the cylinder and which rests on the stylus carrier via one of the edges defining the transition between the flat side and the cylindrical portion of the rod. The spring is of the helical type, with two ends, one being secured to the carriage. The locking member further includes a lever, secured to the rod at its pivoting point and which cooperates with the other end of the spring, to generate the blocking force.
In order to simplify the unlocking of the stylus carrier, the column is provided with a stop block against which the lever abuts at the end of its travel, so as to generate an opposite force to the locking force.
In order to facilitate the positioning of the stylus carrier, the slide is closed by a stop at its opposite end to that in which the stylus carrier is engaged.
Advantageously, the apparatus includes a column, on which the carriage is slidably mounted, and a counterbalance weight, which is also slidably mounted on the column and which is connected to the carriage, in order to balance them. Such a construction allows the stylus to be placed in any position, and it remains there thanks to the counterbalance weight. However, when during a measurement, the stylus carrier has to be changed, the balance of the carriage and the counterbalance weight may be destroyed. In order to overcome this difficulty, the stylus carrier may include cut out portions which lighten it. Consequently, it is possible to use stylus carriers of different types, without having to perform any particular adjustment.
In a particularly advantageous embodiment, the measuring apparatus further includes an electronic measuring arrangement, a base, a column secured to the base, on which the carriage is slidably mounted. In this embodiment:
the column carries a measuring scale;
the carriage is provided with a reader cooperating with the scale and connected to the electronic measuring arrangement; and
the stylus, which is movable along an axis parallel to the direction of engagement of the bar in the slide, is provided with electrically controlled measuring means, which are also connected to the electronic arrangement.
The movement amplitude of a stylus as defined above is unfortunately very limited. This is why, in order to allow a measurement of the same order of magnitude as is allowed by the movement of the carriage, in a particular embodiment, the apparatus further includes a ruler, oriented parallel to the axis of mobility of the stylus, and a reader head provided with electrically controlled measuring means cooperating with the ruler, one secured to the base and the other to the support. In this apparatus, the measuring means associated with the stylus and the head are connected to the electronic measuring arrangement which is arranged to add the measured values, thus giving the value of the dimension measured along an axis perpendicular to the movement of the carriage and parallel to the direction of mobility of the stylus.